In recent years, concomitant with the advancement of techniques for manufacturing microstructures on substrates, so-called micromachines (Micro Electro-Mechanical Systems, hereinafter referred to as “MEMS”) and compact apparatuses incorporating MEMSs have drawn attentions. The MEMS is a device composed of an oscillator, which is a movable structural element, and a semiconductor integrated circuit or the like which controls the drive of the oscillator and which is electrically and mechanically coupled therewith. In addition, the oscillator is incorporated in part of the device, and the drive of the oscillator is electrically performed using the Coulomb force or the like between electrodes.
Of the MEMSs as described above, in particular, devices formed using a semiconductor process have the following various features. That is, for example, the devices each require a small area, can realize a high Q value (quality indicating the sharpness of resonance of an oscillation system), and can be integrated with another semiconductor device (integration); hence, the use as a high-frequency filter for wireless communication has been proposed (for example, see C. T.-C. Nguyen, “Micromechanical components for miniaturized low-power communications (invited plenary),” proceedings 1999 IEEE MTT-S International Microwave Symposium RF MEMS Workshop, Jun. 18, 1999, pp. 48-77).
Incidentally, when a MEMS is integrated with another semiconductor device, the structure has been proposed in which encapsulation is performed for the oscillator, which is a part of the MEMS, so that a wiring layer or the like is further provided above the oscillator (for example, see Japanese Unexamined Patent Application Publication No. 2002-94328 (p. 7 and FIG. 10)). However, when the oscillator is encapsulated, a hollow structure must be formed around the oscillator, that is, it is required that a space around a movable portion of the oscillator is ensured so as to place the oscillator in a movable state. For ensuring the space around the movable portion described above, in general, so-called sacrifice-layer etching is performed.
The sacrifice-layer etching is etching in which a thin film is formed beforehand around the movable portion of the oscillator and is then removed by etching so as to form the space (gap) around the movable portion. In addition, the thin film formed around the movable portion for sacrifice-layer etching is called a sacrifice layer.
However, the integration of the MEMS with another semiconductor device has various problems. In general, for this integration, a process for manufacturing the MEMS (particularly, the oscillator thereof) is performed in a final step which is added to a manufacturing process (such as a CMOS process) of said another semiconductor. Accordingly, in the process for manufacturing the MEMS, in order to avoid adverse influences on the semiconductor device which is already formed, a high-temperature process cannot be performed. That is, the oscillator must be formed at a low temperature, and as a result, the process therefor may not be easily performed in some cases.
On the other hand, when the part of the MEMS, that is, the oscillator, is encapsulated, a wiring layer or the like may be further formed thereabove, and as a result, even though the oscillator is formed at a high temperature, an adverse influence of the high-temperature process on the wiring layer or the like can be avoided. However, in the case described above, since the space around the movable portion of the oscillator formed by sacrifice-layer etching is vacuum-sealed, a specific packaging technique using an insulating material or the like is required (for example, see Japanese Unexamined Patent Application Publication No. 2002-94328 (p. 7 and FIG. 10). That is, since a packaging step for vacuum sealing is required, manufacturing cannot be easily performed using the existing semiconductor process (such as a CMOS process), and as a result, the production efficiency of a device including the MEMS may be decreased in some cases.
Accordingly, an object of the present invention is to provided a method for manufacturing a micromachine, in which the oscillator, which is the part of the MEMS, is sealed using sacrifice-layer etching in order to achieve easier formation of the MEMS, and in which even in the case described above, removal of a sacrifice layer and sealing can be performed without using any specific packaging technique.